Abstract

Pain, in both animals and humans, can induce wide-ranging biological consequences. In farmed livestock, two of the most important of these consequences are the potential impacts of pain on immune function and growth. In humans, the subjective experience of pain is correlated with decreases in immunocompetence and increases in the subsequent incidence of illness. In animals, procedures that can be readily assumed to be painful, and which produce behavioural and physiological stress responses, can cause immunosuppression and reductions in feed intake. Although transient pain may temporarily enhance immune function, chronic pain is immunosuppressive. The deleterious effects of pain on animal growth appear linked to the inflammatory response that accompanies tissue injury and to the direct impact of pain on feeding behaviour. The pro-inflammatory cytokines, (interleukin-1, interleukin-6 and tumour necrosis factor alpha) contribute to tissue catabolism, and act directly at the central nervous system to induce anorexia and lethargy. Although these behavioural and metabolic responses to painful conditions are adaptive in the short term, allowing the animal to rest its injury and mobilise body reserves to aid healing, ongoing pain responses have obvious negative consequences for animal productivity. Therefore, both animal welfare and productivity considerations suggest that the relief of any ongoing pain, as well as of acute pain, is important.

AD, Fisher

Proceedings of the New Zealand Society of Animal Production, Volume 62, Palmerston North, 363-367, 2002